The present invention relates to a battery-powered apparatus for driving a magnetic disk for storing information therein and retrieving the stored information therefrom.
A magnetic disk drive system is known, wherein a drive motor for rotating the magnetic disk is powered by a battery. The line voltage of the battery is gradually lowered as the cumulative operation time increases. A drop of the battery voltage level below a certain lower limit will make it impossible to achieve a stable operation of the drive motor, and consequently the voltage drop will lead to instability of rotation of the magnetic disk. In such a magnetic disk drive, however, data writing and reading operations on the magnetic disk are continued even after the rotating operation of the magnetic disk has become unstable due to voltage drop of the battery, as long as an access to the magnetic disk is possible at lowered voltage levels of the considerably exhausted battery.
Unstable rotations of the magnetic disk during data storage and retrieval may possibly cause data writing and reading errors. In the absence of suitable means for indicating the occurrence of such errors, the operator who is engaged in the data storage or retrieval may not recognize the presence of the errors due to the voltage drop of the battery to power the disk drive motor. This may lead to a problem that correct information is not written on or read from the magnetic disk.